Forces
Springs and Hooke’s Law
To explain how force and extension are related for a spring and recognise when Hooke’s law no longer applies.
What you will learn
What extension means for a spring
How force and extension are linked by Hooke’s law
How to calculate spring constant
How to recognise the limit of proportionality
What happens when a spring is stretched too far
Explanation
Extension is stretched length minus original length. Within the limit of proportionality, force is proportional to extension and F = ke. Elastic deformation is reversed when the force is removed; inelastic deformation leaves a permanent change. The limit of proportionality and elastic limit are not identical definitions. Example: A spring has k = 300 N/m and extension 4 cm within its proportional range. Calculate force. e = 4 cm = 0.04 m; F = ke = 300 × 0.04 = 12 N. Give a reason. Compare cases.